A lockdown has been lifted at an Alabama military installation after no shooter was found Tuesday.

Officials were investigating the possibility of a hoax.

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The lockdown created confusion and worried many people with friends and family at the Redstone Arsenal installation near Huntsville, where more than 30,000 government employees, civilians and contractors work daily. After a tweet advised workers of a possible active shooter and told them to "run hide fight" many people took to social media to offer their prayers and await updates.

Authorities said that 911 emergency calls prompted the lockdown but after a thorough search, no immediate threat was located.

Christopher Colster, a spokesman for Redstone Arsenal in Hunstville, said that officials do not believe there is an ongoing threat. No injuries or arrests have been reported.

Colster said a training exercise was ongoing that was supposed to end Wednesday.

Officials had said on Facebook that an active shooter training exercise was planned for this week. But Colster would not say whether the active shooter report was part of that exercise, adding: “I really can’t say at this point what happened. I’m not sure myself.”

"My office is being updated about the situation @TeamREDSTONE I will continue to closely monitor and pray for a peaceful and quick resolution."

More than 30,000 government employees, civilians and contractors work daily at Redstone. NASA's Marshall Space Flight Center, which oversees rocket propulsion operations, also is located at Redstone.

Madison, Ala., posted about the situation, asking "friends and family who work on the arsenal to stay safe and find a place to hide."